Question

A solution prepared by adding 0.17 g of a
polymer to 0.6 L of toluene (methylbenzene, a
common solvent) showed an osmotic pressure
of 0.808 Torr at 21â—¦C. What is the molar mass
of the polymer?
Answer in units of g/mol.

Answer 1

pi = MRT
pi = 808 torr. Convert to atm.
M = ?
R = 0.08206
T = 21 C. Convert to kelvin.

Solve for molarity = M
Then M = mols/L with L = 0.6
Find mols. Finally, mol = grams/molar mass. You know mols and grams, solve for molar mass. Post your work if you get stuck.

Answer 2

I do not understand how to get the last step.

Answer 3

You solved for M in pi = MRT and you want to find molar mass.

M = mols/L. You know M from the above, you know L (0.6), solve for mols like this. mols = M x 0.6 = ?. Knowing mols, use mols = grams/molar mass, then molar mass = grams/mols.